Here's my submission for the z-axis. All attempts for accuracy have been made, however I would highly suggest that all measurements be double checked.
The bolt head measurements are from some bolts that I have, however I found three different sizes so I went with the one I had the most of and that seemed to be the most common.
These ideas were what I was thinking of for a future mod to my existing machine or for a new machine. I drew these with the dimension as suggested by Joe.
Hopefully the drawings will provide some useful information.
Saved as version 2004
z_axis.dwg
Saved as version 2000
z_axis_2000.dwg
Bob